Piston



H. H. DILLON Oct. 27, 1936.

PISTON Filed Jan. 13, 1953 3 mentor HA POLE .D/ZA O/V (Ittorneg 5 patella-1iv a. 27, 1936 UNITED STATES Harold HEJillon,

mesne assignments, to The Cleveland Trust Company, Cleveland, Ohio, a corporation of Ohio, as trustee Application January 13, 1933, Serial No. 651,525

Claims. (01.309-11) ent No. 1,926,611 and Frank Jardine, Serial No.

619,947, filed June 29, 1932, now Patent No. 1,939,778.

I In the type of piston disclosed in said applications the excess thermal expansion of the light metal alloy of which the piston is composed over the thermal expansion of the cylinder in'which the piston reciprocates is absorbed in part by a substantially'vertical slot in the minimum thrust face of the piston terminating above the bottom of the piston skirt and intersecting a substantially horizontal slot separating the upper edge of the minimum thrust face only from the ring flange of the piston head, and in part by the contour of the piston. This novel arrangement provides an extremely simple piston which may be readily and easily cast in permanent molds and machined to final form, and one which compensates for the excess expansion of the light metal alloy while permitting a close flt without danger of slapping when the piston is cold, while at the same time retaining a full solid maximum thrust face with freedom for maximum heat flow from the head to the piston skirt, and avoiding excessive bending or flexing of theskirt under lateral thrust loads and consequent permanent deformation of the split portions of the skirt.-

It has been found that although this type of piston has solved in a,-simple and economical manner most of the problems of piston design resulting from the unequal thermal expansion of a light metal alloy piston and the cylinder in which the piston is employed, a tendency exists in some cases for the head portion of the piston tosplit off from the skirt and wrist pin'boss portion by breaking open the metal in a continuation of the horizontal slot between the upper edge of the minimum thrust face and the ring flange. This has apparently been due in part to the different action of the metal during expansion on the opposite sides of the piston, since on the maximum thrustface side and in the portion above the wrist pin bosses thepiston is a solid trunk type piston.

with a continuous integral connection between the ring flange and the skirt, whereas on the opposite side or minimum thrust face side of the piston the upper edge of the skirt and the lower edge of the ring flange are separated. Whena certain increment of circumferential expansion at the top of the skirt has been absorbed by the substantially vertical split, the upper edges of the split portions of the minimum thrust face have been swung like tongues along lines substantially intersectingthe ends of the horizontal slot, and

PATENT OFFICE PISTON v Cleveland, Ohio, assignor, by

the vertical axis of the piston has been moved slightly from the vertical axis of the cylinder in the direction toward the split side of the skirt.

This tendency has apparently also been due in part to the inertia and power loads transmitted between the head and the wrist pin.

I have discovered that this tendency toward splitting off of the piston head maybe overcome, without increasing the weight of the piston or introducing complex internal contours which might tend to interfere with the simple manufacture of a piston in permanent molds, by providing the interior of the piston head and the ring flange above the wrist pin bosses with a reenforcing bridge oflfset'toward the split side of the piston from the vertical plane through the wrist pin axis. Preferably this reenforcing-brldge is offset a sufiicient distance so as to be disposed entirely on the slotted side of the piston with respect to this vertical plane, and is of sufilcient cross section to evenly distribute about this vertical plane the power and inertia loads transmitted between the head and the wrist pin. In

this manner the vertical legs of the reenforcing bridge are disposed closely adjacent the ends of the horizontal slot, and the intersection of the ring flange and the skirt on the maximum thrust side of the piston for a full 180 degrees is uniform, thereby reducing the distorting forces arising from the movement of the metal when expansion is absorbed by closing of the substantially vertical slot.

In the accompanying drawing which illustrates, a preferred embodiment of the invention:

Figure 1 is a side elevation of the piston; Figure 2 is a vertical sectional view taken substantially on the line 2-2 of Figure 1;

' Figure 3 is a vertical sectional view taken on the line 3-3 of'Figure 2;

Figure 4is a horizontal sectional view taken on the line 4-4 of Figure 1. v

For purposes of clearance, the description is made on the assumption that the long axis of i the piston is vertical, as illustrated in the drawing, altho that axis may not be vertical when the piston is in its cylinder, as for example, in a V- type engine where thelong axis of thepiston may be inclined at an angle of degrees to a vertical line.

Referring to the drawing the piston illustrated is generally of the full trimk type piston includjoined bya horizontal rib l6 extending across the underside of the piston head. The ribs 15 extend as shown from the wrist pin bosses upwardly to the piston head on one side of the vertical plane through the wrist pin axis. The vertical ribs IS on one side merge into bosses IT. A thickened portion or pad i8 is formed in the inner'surfaces of one thrust face. i

The piston is preferably cast in permanent molds or the like in the same manner as a full trunk type piston; the ofiset ribs i5 and Hi, the

fiange. This thrust face, indicated by the numeral 24, is called the minimum thrust face and is designed to be arranged in the engine to receive the lateral thrust of the compression stroke. The opposite thrust face 25, which remains continuously integral with the ring flange except the suitable oil holes and the like when desired, is called the maximum thrust face and is arranged in the engine to receive the lateral thrust of the power vstroke. Holes 2i and 22 are drilled through the minimum thrust face 24 and through the reenforcement l8 and form the upper and lower termini, respectively, of a substantially vertical slot 23. The hole 2! intersects the horizontal slot 20 as shown in Figure 1 and the hole 22 is disposed within the lower end of the pad I8 as shown in Figure 3.

As illustrated in Figures 2and 4 the holes I!) which form the'ends of the horizontal slot 20 open through the bosses I] immediately adjacent the vertical ribsi5 so "that the metal at the ends of the hdrizontalslot is reenforced against splitting by the radial thickness of the ribs IS. .The vertical ribs i5 and the horizontal ribs l6 form as a whole a reenforcing bridge work extending upwardly from each wrist pin boss and across on the under side of the head, all disposed onthe slotted side of the piston with respect to the vertical plane through the wrist pin axis.

In operation the ribs l5 serve to carry thegreater part of the compression and tension loads between the wrist pin bosses l4 and the head ii. The compression loads are caused by the explosive forces of: the gas .above the piston head which must be transmitted to the wrist pin journalled in the bosses l4 and also by inertia, while the tension loads are produced entirely by inertia when the direction of motionof the piston is reversed. Without the reenforcing bridge a compression load applied to the entire top of the piston head would tend to rock the top downwardly on the slotted side, since the ring flange and skirt are integral about one side of the piston and separated by the slot 20 on the other side. Likewise the tension loads would tend, without the reenforcing bridge work, to spread the horizontal slot 20,- since the piston head on that side is not connected to the skirt and on the opposite side is continuously integral with thetop of the skirt. Obviously, exactly the same efiect occurs when the usual'reenforcing ribs for transmitting the loads from the head to the wrist pin bosses are employed, disposed directly in the vertical plane through the wrist pin axis.j

With the improved construction disclosed herein this tendency to rock the piston head from the compression and tension loads is counteracted by the fact that the greater portions of these loads are transmitted through the ribs i5 spaced to.- ward the slotted side of the piston from the vertical plane. Preferably this spacing is suflicient and the cross section of the ribs I5 is suificient to uniformly distribute the loads to the two sides of the piston and to completely counteract the tendency of the head to rock with respect to the skirt.

Likewise the offsetting of the reenforcing bridge work minimizes the stresses set up at the ends of the horizontal slot 20 by the non-uniformity of the movement of the metal on the opposite sides' of the piston which results from the fact that substantially all of the circumferential expansion of the top of the piston skirt is absorbed on one side by the closing of the vertical slot 23. As a consequence this improved structure practically eliminates the previously existing tendency in this type of piston for the head of the piston to separate from the skirt in use.

It will be understood thatpreferably the piston skirt is provided with an unsymmetrical contour as disclosed in the aforesaid co-pending applications of Jardine and Moore, although the present invention is not limited to this feature or to the exact slotting arrangement disclosed, since it is useful in any type of piston which is unsymmetrically slotted so as to create a tendency for the head to break off from the skirt under the power of inertia loads or the stresses setup by thermal expansion.

As shown by the drawing, the reinforcing ribbing, as a unit, is offset from the vertical plane thru the wrist pin bosses toward the slotted side of the piston. Since the ribbing is so offset, its center of mass is likewise offset and in the same direction.

What I'claim is: v

1. A piston composed of a light metal alloy and including a head having a depending ring flange and a skirt, diametrically opposed wrist pin bosses in the skirt, the upper edge of said skirt being continuously integral with the lower edge of the ring flange on one side of a vertical plane through the axis of the wrist pin bosses and being partially separated therefrom on the opposite side of such plane by a substantially horizontal slot, and reenforcing ribs integral with said wrist pin bosses and extending up to and integral with said head offset from the vertical plane through the axis of the wrist pin bosses toward the slotted side of the piston, the connection between said skirt and ring flange being substantially uniform in thickness on the opposite side of the piston.

2. A piston composed of a light metal alloy and including a head having a depending ring flange and a skirt, diametrically opposed wrist pin bosses in the skirt, the upper edge of said skirt being continuously integral with the lower edge of the ring flange on one side of a vertical plane through the axis of the wrist pin bosses and being partially separated, therefrom on the opposite side of such plane by a substantially horizontal slot,

work being ofiset from the vertical plane through the axis of the wrist pin bosses toward the slotted side of the piston.

3. A piston composed of a light metal alloy and including a head having 8. depending ring flange, a substantially cylindrical skirt carrying axially aligned wrist pin bosses, said skirt on one side of the 'vertical plane through the axis of the wrist pin bosses being partially separated from said ring flange by a substantially horizontal slot and having a substantially vertical slot intersecting said horizontal slot and terminating above the lower end of the skirt, the upper edge of said skirt being continuously integral with said ring flange on the other side of such plane through a connection of substantially uniform thickness, and reenforcing ribs integral with said wrist pin bosses and said head oflset from the vertical plane through the axis of the wrist pin bosses toward the slotted side of the piston.

4. A piston composed of a light metal alloy and including, a head having a depending ring flange, a substantially cylindrical skirt carrying axially aligned wrist pin bosses, said skirt on one piston head, all of said re-e'nforcing bridge work I the' piston.

being oifset from the vertical plane through the 'axis of the wrist pin bosses toward the slotted side of the piston.

5. An internal combustion engine piston composed of a. light metal alloy consisting of a head having'a depending ring flange and a substantially cylindrical skirt carrying axially aligned wrist pin bosses, the upper edgeof said skirt being partially integral with. the lower edge of said ring flange and being partially spaced therefrom,

= with a greater extent of the integral connection between the skirt and the ring flange on one side of the piston with respect to the vertical plane through the axis of the wrist pin bosses than on the other side of the piston, and vertical reenforcing ribs integral with said wrist pin bosses and with the ring flange and head, all of said ribs being ofiset toward .said last mentioned side of 6; A piston for lntemal combustion engines composed of a light'metal alloy and including a head having a depending ring flange and a skirt having opposed thrust faces and carrying axially aligned wrist pin bosses, the upper edge of said skirt being partially'integral with the lower edge of said ring flange, one of the thrust faces of said skirt being slotted, and substantially vertical reenforcing ribs integral with said wrist pin bosses and with said ring flange and said head, all of said ribs being oflset toward the slotted thrust face of said skirt from the vertical plane through the axis of said wrist pin bosses.

7. A one-piece aluminum alloy piston for an internal combustion engine comprising a head having a substantially cylindrical depending ring flange, a skirt having wrist pin bosses formed therein and having its upper edge continuously .integral with said ring flange on one side of a vertical plane through the wrist pin axis, and partially separated from said ring flange by a hori-\ zontal slot on the other side of such plane, whereby a smaller cross-sectional area of metal for transmitting loads between the head and wrist pin bosses exists on the slotted side of said piston than on the opposite side, and re-enforcing ribs integral with said wrist pin bosses, said ring flange, and said head ofiset from the vertical plane through the wrist pin axis toward the slotted side of 'the piston to substantially equalize the cross-sectional area of the metal connecting the head and skirt on theopposite sides of such vertical plane.

8. In internal combustion engine piston composed of a light metal alloy consisting of a head having a depending ring flange and a substantially cylindrical skirt carrying axially aligned wrist pin bosses, the upper edge of said skirt being partially integral with the lower edge of said ring flange and being partially separated therefrom, with a greater extent and cross-sectional area of the integral connection between the skirt and the ring flange on one side of the piston with respect to the vertical plane through the axis of the wrist pin bosses than on the other side of the piston, and vertical re-enforcing ribs integral with said wrist pin bosses and with the ring flange and head oiTset toward said last mentioned side of the piston and having a cross-sectional area sufiicient to uniformly distribute the loads between the head and the wrist pin bosses to said two sides of the piston.

9. A one-piece light metal alloy piston for an internal combustion engine comprising a head having a substantially cylindrical depending ring flange, a skirt having wrist pin bosses formed therein and having its upper edge continuously integral with said ring flange on one side of a vertical plane through the wrist pin axis, and partially separated from said ring flange by a horizontal slot on the other side of such plane, whereby a smaller cross-sectional area of metal for transmitting loads between the head and wrist pin bosses exists on the slotted side of said piston than on the opposite side, and re-enforcing ribbing integral with said wrist pin bosses, said ring flange and said head, the center of mass of all of said ribbing as a unit beingofiset from the verticalplane through the wrist pin axis toward the slotted side of the piston, said ribbing comprising a substantially straight rib integral with and projectirm from the underside of said piston head 4 oifset from said vertical plane through the wrist pin axis toward the slotted side of the piston, and downwardly extending ribs integral with said ring flange and with the ends of said first mentioned rib separated therefrom on the opposite side of such plane by a substantially horizontal slot, and reenforcing bridge work comprising a pair of vertically extending ribs connected to the wrist pin bosses and integral with the ring flange and integrally joined by a rib projecting from the underi side of the piston'head, all of said reenforcing bridge work being offset from the vertical plane through the axis of the wrist pin bosses toward the slotted side of the piston.

HAROLD H. DILLON. 

